1. Field of the Invention
This invention relates to the production of a bonded silicon wafer, and more particularly to a method for producing a bonded silicon wafer through steps of an oxygen ion implantation-etching/polishing stop wherein an SiO2/Si interface roughness can be improved by using a silicon wafer for active layer with such a wafer face that an inclination angle θ (compound angle) with respect to a face perpendicular to <100> orientation or <110> orientation of a silicon single crystal ingot is 0°<θ≦0.15°. Moreover, the production method according to the invention is applicable to both of an SOI (Silicon On Insulator) wafer and a DSB (Direct Silicon Bonding) wafer, and can prevent a blue haze in case of the DSB wafer.
2. Description of the Related Art
The SOI wafer has superiority in separation between devices, reduction of parasitic capacity between a device and a substrate and capability of a three-dimensional structure as compared with the conventional silicon wafer. Therefore, it is used in high-speed and low power consumption LSI. As a method of producing the SOI wafer, there is known a bonding method wherein two silicon wafers provided with an oxide film are bonded to each other and thereafter grinding and polishing are conducted to form an SOI layer (active layer). In the bonding method is included a Smart Cut (registered trademark) method (see JP-A-H09-116125 and JP-A-2000-124092).
In the SOI wafer are required thinning and thickness uniformization of the SOI layer (active layer). Therefore, a new way has been developed. This way allows the thinning and thickness uniformization of the SOI layer (active layer) by bonding a silicon wafer for active layer having an oxygen ion implanted layer to a silicon wafer for support layer, subjecting to a heat treatment to convert the oxygen ion implanted layer into an SiO2 layer, grinding and polishing from a side of the silicon wafer for active layer to the SiO2 layer, and thereafter removing the SiO2 layer (see WO 2005/074033). The oxygen ion implanted layer serves as an etching/polishing stop layer.
Recently, the thickness of an oxide film as a BOX layer is thinned with the miniaturization and low power consumption of devices, and further the development of DSB wafer by directly bonding without the BOX layer (oxide film) is also conducted. When the wafers are directly bonded without an oxide film, the usual cleaning (SC1) is carried out before the bonding of silicon wafer for active layer and silicon wafer for support.
However, in the method of producing a bonded silicon wafer by using an etching/polishing stop layer described in WO 2005/074033, there are the following problems.
(1) The interface roughness between a layer containing SiO2 particles as a polishing stop layer or a continuous SiO2 layers and a silicon substrate is large, and hence the surface roughness of a bonded wafer as a final product becomes large.
(2) For this end, after the formation of an SOI structure, it is required to conduct polishing of not less than 0.1 μm or a high-temperature heat treatment above 1200° C. for more than 1 hour as an additional process for improving the surface roughness. The polishing of not less than 0.1 μm leads to deteriorate the thickness uniformity of the SOI layer as a final product. On the other hand, the high-temperature heat treatment leads to cause the quality loss such as slipping or the like, and the increase in cost.
As to (1), there is caused a similar problem in the bonding method using the etching/polishing stop layer for not only SOI wafer but also DSB wafer.
Furthermore, the DSB wafer has a problem of a blue haze that the wafer surface appears blue. In the SOI wafer, a color is observed depending on the thickness of SOI by optical interference with a buried oxide film, but if the blue haze is generated, a different color may be observed due to the overlap of the interference light with the blue haze, which is regarded as a defect. In any case, it is desired to solve these problems.